1. Field of the Invention
This invention relates to a device and method for driving a speaker and is suitably applied to a speaker unit having a signal amplifier.
2. Description of the Related Art
Referring to FIG. 1, a speaker unit 1 of one type amplifies with a signal amplifier 3 an audio signal S1 reproduced by a signal source 2, and outputs sounds based on the obtained audio signal S2 from a speaker 4, the signal source 2 being an external reproduction device such as a Mini Disc (MD) player or a tuner.
For example, as shown in FIG. 2, the cone speaker 4 has a cone diaphragm 10 with both ends open. The outer opening of the cone diaphragm 10 is supported by an edge 12 formed in a frame 11 via a gasket 13, and its inner opening is supported by a damper 14 attached to the frame 11, so that the cone diaphragm 10 can vibrate forward and backward with respect to the frame 11.
Fixed to the inner opening of the cone diaphragm 10 is a cylinder voice coil bobbin 16 having a voice coil 15 being a lead wire wounded therearound. In addition, a hemisphere head cap 17 is attached so as to cover the inner opening of the cone diaphragm 10.
Attached to the bottom of the frame 11 is a magnetic circuit 18 for vibrating the cone diaphragm 10 forward and backward. This magnetic circuit 18 has a disc yoke 19 with a column pole piece 19A formed at the center, a ring magnet 20, and a ring plate 21, which are fixed to each other.
While the magnetic circuit 18 is attached to the bottom of the frame 11, the voice coil bobbin 16 having the voice coil 15 wounded therearound is kept out of touch in a gap g between the pole piece 19A and the plate 21.
In addition, in this speaker 4, a connector 22 having a plurality of connecting terminals is provided at a projecting part 11P formed at the bottom of the frame 11, so that reproduction devices (that is, the signal source 2 of FIG. 1) such as an external MD and a tuner can be connected to the connecting terminals with lines via the signal amplifier 3 (FIG. 1). A harness is drawn from each connecting terminal of the connector 22 and is conductive to the lead wire 15A of the voice coil 15.
When the speaker 4 receives the audio signal S2 from the signal amplifier 3, a magnetic field according to an impressed current based on the audio signal S2 is generated in the magnetic gap g between the pole piece 19A and the plate 21 of the magnetic circuit 18. Therefore, sound waves based on the audio signal S2 is generated while the cone diaphragm 10 vibrates forward and backward because of attraction and repulsion of the voice coil 15 existing in the magnetic gap g (For example, refer to Japanese Patent Application Laid-open No. 53-48087).